Supplementary Figure 1 Morpholigical properties of TiO 2-x SCs. The statistical particle size distribution (a) of the defective {001}-TiO 2-x SCs and

Transcription

1 Supplementary Figure 1 Morpholigical properties of TiO 2-x s. The statistical particle size distribution (a) of the defective {1}-TiO 2-x s and their typical TEM images (b, c).

2 Quantity Adsorbed (cm 3 /g STP) dv/dlog(d) Pore Volume (cm 3 /g nm) Intensity (a.u.) (a) {1}-TiO 2-x {1}-TiO 2 {11}-TiO 2 PC ( ) 15.6 Adsorption Desorption (b) Pore diameter (nm) {1}-TiO 2-x Relative Pressure (P/P ) Supplementary Figure 2 Crystal phase and surface area of different TiO 2 catalysts. XRD pattern (a) and BET spectra (b) of the {1}-TiO 2-x s, {1}-TiO 2 s and {11}-TiO 2 PCs.

3 Supplementary Figure 3 Morphological properties of commercial TiO 2. Typical TEM images of the {11}-TiO 2 PCs reference (a, b).

4 Quantity Adsorbed (cm 3 /g STP) dv/dlog(d) Pore Volume (cm 3 /g nm) Quantity Adsorbed (cm 3 /g STP) dv/dlog(d) Pore Volume (cm 3 /g nm) (a) Pore diameter (nm) Adsorption Desorption Relative Pressure (P/P ) (b) Pore diameter (nm) Adsorption Desorption Relative Pressure (P/P ) Supplementary Figure 4 Surface area of two TiO 2 references. BET spectra of the {11}-TiO 2 PCs (a) and {1}-TiO 2 s (b).

5 Intensity (a.u.) Intensity (a.u.) Intensity (a.u.) Survey {1}-TiO 2 {1}-TiO 2-x (a) Binding energy (ev) ev Zn 2p (b) {1}-TiO 2-x Binding energy (ev) ev Zn 2p (c) {1}-TiO Binding energy (ev) Supplementary Figure 5 XPS spectra of different TiO 2 catalysts. XPS spectra of the survey and the Zn 2p of the {1}-TiO 2-x s (a, b) and the {1}-TiO 2 s (a, c).

6 Current ( A) Current ( A) Current ( A) (a) {11}-TiO 2 PC Potential (V, versus E) {1}-TiO 2-x (c) Potential (V, versus E) Current ( ) (b) {1}-TiO Potential (V, versus E) {1}-TiO 2-x /rgo (d) Potential (V, versus E) Supplementary Figure 6 ORR behaviors of different TiO 2 catalysts at various rotating rates. Linear voltammetry in O 2 -saturated.1 M aqueous KOH electrolyte solution at a scan rate of 1 mv s -1 at different RDE rotation rates on the {11}-TiO 2 PC (a), {1}-TiO 2 (b) and {1}-TiO 2-x (c) and {1}-TiO 2-x supported by home-made rgo (d).

7 j -1 (ma -1 cm 2 ) j -1 (ma -1 cm 2 ) j -1 (ma -1 cm 2 ) {11}-TiO 2 PC (a) {1}-TiO 2-1/2 (rpm -1/2 ) (b) {1}-TiO 2-x (c) -1/2 (rpm -1/2 ) /2 (rpm -1/2 ) Supplementary Figure 7 Calculation results from RDE tests. K-L plots (i -1 vs. ω -1/2 ) derived from the linear voltammetry in O 2 -saturated.1 M aqueous KOH electrolyte solution at a scan rate of 1 mv s -1 at different RDE rotation rates on the {11}-TiO 2 PC (a), {1}-TiO 2 (b) and {1}-TiO 2-x (c).

8 Electron transfer number (n) Peroxide percentage (%) {1}-TiO 2-x n 2 HO rpm Potential (V, versus E) Supplementary Figure 8 Calculation results from RRDE tests. Peroxide percentage and electron transfer number n of ORR on the defective {1}-TiO 2-x s in O 2 -saturated.1 M aqueous KOH electrolyte solution at a scan rate of 1 mv s -1 with a rotation rate of 4 rpm.

9 Current ( A) Current ( A) Current ( A) -1 (a) {11}-TiO -7 2 PC/C (b) Potential (V, versus E) {1}-TiO 2 /C (c) Potential (V, versus E) {1}-TiO 2-x /C Potential (V, versus E) Supplementary Figure 9 ORR behaviors of different TiO 2 /C catalysts at various rotating rates. Linear voltammetry in O 2 -saturated.1 M aqueous KOH electrolyte solution at a scan rate of 1 mv s -1 at different RDE rotation rates on the {11}-TiO 2 PC (a), {1}-TiO 2 (b) and {1}-TiO 2-x (c) supported by commercial carbon.

10 -Z'' (ohm) -Z'' (ohm) -Z'' (ohm) 7k 6k 5k 4k 3k 2k {11}-TiO 2 PC {1}-TiO 2 {1}-TiO 2-x (a) 1k 2.k 16.k 1k 2k 3k 4k 5k 6k 7k 8k {11}-TiO 2 PC {1}-TiO 2 {1}-TiO 2-x Z' (ohm) -.2 V (b) 12.k 8.k 4.k. 3.k 25.k 2.k 1k 2k 3k 4k {11}-TiO 2 PC {1}-TiO 2 {1}-TiO 2-x Z' (ohm) -.4 V (c) 15.k 1.k 5.k. 1k 2k 3k 4k 5k Z' (ohm) -.6 V Supplementary Figure 1 Electronic properties of different TiO 2 catalysts at various applied bias. EIS plots of the three anatase TiO 2 surfaces under the external bias of -.2 V/E (a), -.4 V/E (b) and -.6 V/E (c). 1

11 Supplementary Table 1 Comparison of ORR specific activities of different TiO 2 catalysts in O 2 -saturated.1 M aqueous KOH electrolyte solution (scan rate: 1 mv s -1, rotation rate: 4 rpm). ORR Catalyst Specific Activity ( 1-3 ma cm -2 ) -.35 V -.4 V -.45 V {11}-TiO 2 PC {1}-TiO {1}-TiO 2-x {11}-TiO 2 PC/C {1}-TiO 2 /C {1}-TiO 2-x /C {1}-TiO 2-x /rgo

12 Supplementary Table 2 O-O bond length in the oxygen substrate and its key intermediates in ORR on {11}-TiO 2, {1}-TiO 2 and {1}-TiO 2-x. Anatase TiO 2 surface O 2 (Å) O 2 2- (Å) OOH - (Å) {1}-TiO {1}-TiO 2-x {11}-TiO

13 Supplementary Table 3 Calculated thermodynamic properties (ΔG) and energy barrier (E a ) in ORR on {1}-TiO 2, {1}-TiO 2-x and {11}-TiO 2, at K and 1 atm. ORR Step {1}-TiO 2 {1}-TiO 2-x {11}-TiO 2 ΔG E a ΔG E a ΔG E a O 2 * + 2e - O 2-2 * O 2-2 * + H 2 O OOH - * + OH OOH - * O* + OH O* + H 2 O + e - OH* + OH OH* + e - OH Total

14 Supplementary Note 1: ORR Properties on the Different Surfaces of Anatase TiO 2. To date, the O 2 adsorption configurations on {11}-TiO 2 and {1}-TiO 2 have been studied extensively. It is generally agreed that {1}-TiO 2 is relatively more active for O 2 adsorption than {11}-TiO 2, and also the 5-fold coordinated Ti 4+ surface ions are the active site for O 2 adsorption site 1. In this study, to accurately understand the possible contribution of oxygen vacancy to ORR, we first modeled the O 2 adsorption onto a 5-fold coordinated Ti 4+ surface ion with two Ti-O bonds on {1}-TiO 2 and {1}-TiO 2-x for comparison (Table 1). For {1}-TiO 2, O 2 was weakly bound, with a low ΔE ads of 1.3 ev, compared to that onto {1}-TiO 2-x with a much higher ΔE ads of ev. Solid-liquid interfacial adsorption is usually the essential first step in heterogeneous catalysis 2. This result indicates that the O 2 adsorption capacity onto {1}-TiO 2 could be significantly enhanced by crystal oxygen vacancy. It is widely agreed that adsorbed O 2 is initially reduced to O 3 2, which is the precursor of other further reduced active species, such as O 2 2 and HOO. Moreover, on metal oxide catalyst surface, the ORR in alkaline media is generally proposed to proceed through the chained steps including peroxide and oxide formation, hydroxide displacement, and hydroxide regeneration 4-6. Thus, the ORR mechanism on anatase TiO 2 surface could be described in Fig. 7a, similar to the series two-electron pathway of ORR on metal catalysts 7, and the key intermediates of O 2, O 2 2, HOO and OH were detected by in situ infrared measurements 8. The key intermediates of ORR on anatase TiO 2 surfaces involve the active 14

15 species of O 2 *, O 2 2 *, HOO *, OH* and O* (*: adsorbed state). Their geometry structures of adsorption configuration on {1}-TiO 2, {1}-TiO 2-x and {11}-TiO 2 were thermodynamically optimized, as illustrated in Fig. 6, to understand their catalytic activities. As anticipated, all the O-O bonds in O 2 *, O 2 2 *, HOO * were elongated over that of O 2 (Supplementary Table 2), indicating their thermodynamic activation for further ORR. The ORR could be divided into two stages (Fig. 7a): reducing absorbed O 2 to adsorbed peroxide and peroxide decomposition, followed by the regeneration of hydroxide from absorbed oxide. Supplementary References 1. Mattioli, G.; Filippone, F.; Bonapasta, A. A., Reaction intermediates in the photoreduction of oxygen molecules at the (11) TiO 2 (anatase) surface. J. Am. Chem. Soc. 128, (26). 2. George, C.; Ammann, M.; D Anna, B.; Donaldson, D. J.; Nizkorodov, S. A., Heterogeneous photochemistry in the atmosphere. Chem. Rev. (In the press) DOI: 1.121/cr5648z (215). 3. Wang, Z. H.; Ma, W. H.; Chen, C. C.; Ji, H. W.; Zhao, J. C., Probing paramagnetic species in titania-based heterogeneous photocatalysis by electron spin resonance (ESR) spectroscopy-a mini review. Chem. Eng. J. 17, (211). 4. Suntivich, J.; Gasteiger, H. A.; Yabuuchi, N.; Nakanishi, H.; Goodenough, J. B.; 15

16 Shao-Horn, Y., Design principles for oxygen-reduction activity on perovskite oxide catalysts for fuel cells and metal-air batteries. Nat. Chem. 3, (211). 5. Cheng, F. Y.; Chen, J., Metal-air batteries: from oxygen reduction electrochemistry to cathode catalysts. Chem. Soc. Rev. 41, (212). 6. Cheng, F. Y.; Zhang, T. R.; Zhang, Y.; Du, J.; Han, X. P.; Chen, J., Enhancing electrocatalytic oxygen reduction on MnO 2 with vacancies. Angew. Chem. Int. Edit. 52, (213). 7. Farberow, C. A.; Godinez-Garcia, A.; Peng, G. W.; Perez-Robles, J. F.; Solorza-Feria, O.; Mavrikakis, M., Mechanistic studies of oxygen reduction by hydrogen on PdAg(11). ACS Catal. 3, (213). 8. Nakamura, R.; Imanishi, A.; Murakoshi, K.; Nakato, Y., In situ FTIR studies of primary intermediates of photocatalytic reactions on nanocrystalline TiO 2 films in contact with aqueous solutions. J. Am. Chem. Soc. 125, (23) 16